1. Field of the Invention
The present invention relates to a technology for retracting a head on a storage medium by detecting a fall of a storage device, with a capability of preventing a degradation of performance when a continuous vibration is erroneously detected as the fall.
2. Description of the Related Art
A magnetic disk drive (storage device) is mainly used as an auxiliary storage device of a general-purpose computer and for a business-purpose device that requires high-capacity random access data recording. Furthermore, use of the magnetic disk drive as a general household appliance has increased recently, with an advance of digitalization of household appliances and an increase of applications to record data such as audio-visual data as digital data (for example, a hard disk video recorder and a portable music reproducing device).
However, when the magnetic disk drive receives a strong impact due to a fall, a head collides with a disk surface and the disk surface gets scratched, and data reading and writing may become impossible. Particularly, falls of the magnetic disk drive while it is in operation cause the magnetic disk drive to become easily out of order. Therefore, when handling a product that includes a magnetic disk drive for a portable application, an attention had to be paid to avoid giving a strong impact to the product.
Japanese Patent Application Laid-Open No. 2002-8336 discloses a technology that uses a fall sensor to prevent damages caused by falls of the magnetic disk drive and retracts the head from the disk surface when a free fall of the magnetic disk drive is detected.
However, the convention technology described above had a problem of degrading performance of the magnetic disk drive since the conventional art simply forcibly retracts the head from the disk surface when erroneously detecting falls of the magnetic disk drive.
Because, in some cases of the conventional method, the fall sensor erroneously detects falls while carrying the magnetic disk drive and during normal use when the magnetic disk drive is not actually falling, and each time the head was retracted from the disk surface.
For example, when the magnetic disk drive is mounted on a personal computer and the personal computer is lifted during transport or used on the lap, a slow cycle vibration is presumably continuously transmitted to the magnetic disk drive. In this case, due to characteristics of the fall sensor, the fall sensor often times erroneously detects the slow cycle vibration as a fall of a certain time. Accesses to the disk for data recording and reproducing are delayed when the head is retracted out from the disk surface each time the fall sensor detects erroneously, and as a result, capability of the personal computer may decrease.